

class Solution {
    // Definition for a binary tree node.
    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode() {}
        TreeNode(int val) { this.val = val; }
        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }
    public String tree2str(TreeNode root) {
        StringBuilder stringBuilder = new StringBuilder();
        tree2strChild(root,stringBuilder);
        return stringBuilder.toString();
    }

    public void tree2strChild(TreeNode t,StringBuilder stringBuilder) {
        if(t == null) {
            return;
        }
        stringBuilder.append(t.val);
        if(t.left != null) {
            stringBuilder.append("(");
            tree2strChild(t.left,stringBuilder);
            stringBuilder.append(")");
        }else {
            if(t.right == null) {
                return;
            }else {
                stringBuilder.append("()");
            }
        }

        if(t.right == null) {
            return;
        }else {
            stringBuilder.append("(");
            tree2strChild(t.right,stringBuilder);
            stringBuilder.append(")");
        }
    }
}